In geology, chalk is a soft, white, porous sedimentary rock, a variety of limestone. The biggest chalk deposits formed in the Cretaceous period, between 130 and 70 million years ago. The White Cliffs of Dover consist of chalk formed during this time. Chalk was first used for drawing as long as 10,000 years ago. However, the word chalk now refers to many different drawing and marking materials. Modern blackboard chalk is normally made from the mineral gypsum while coloured chalk also contains pigment and a non-greasy binder.
We supply Stephens Superline white and coloured chalk sticks.
The word chalk has a number of colloquial usages around the English-speaking world. In betting terminology the “chalk” refers to the favourite: When a bookie recorded bets on a blackboard, the favourite's name would become obscured by chalk dust as the bookie erased and lowered the odds next to its name. Around the London area cocaine is sometimes referred to as “chalk”. In cockney rhyming slang “(ball of) chalk” means “walk”. In San Fransisco Bay Area slang “chalk” can mean “steal”.
The phrase “chalk and cheese”, referring to two thing superficially similar but totally different in character, dates from as early as 1393 when John Gower describes an unscrupulous shopkeeper in his Confessio Amantis thus: “And thus ful ofte chalk for chese he changeth with ful littel cost.” Although some cheeses may bear a passing resemblance to chalk, the popularity of this pair may merely be down to their alliteration.